The present invention serves to produce/generate and monitor electrodynamic interactions between earthed (i.e., electrically grounded) metallic/conductive structures and their ambient electromagnetic (EM) surroundings. The present invention utilizes a novel adaptive resonance-based electromagnetic signal generation and analysis technique, that can be practically utilized as a theft deterrent system for heavy equipment, or for intrusion detection in structures and on long baseline barrier (i.e., fence) applications. The novel and key component in all of these applications is the ability of the system to function with earthed structures (i.e., metal buildings or structures containing large conductive members, fences and tracked or bladed heavy equipment) and in a changing EM ambient.
Unlike other tamper/intrusion detection methods (i.e., ultrasound, vibration, microwave, infrared, laser etc.), the present invention uses the entire structure that is to be monitored as the active sensing element, thereby eliminating zone coverage limitations/problems/issues.
In a typical practical application such as for a xe2x80x9cHeavy Equipment Theft Deterrent/Loss Prevention Systemxe2x80x9d, the present invention is capable of detecting unwanted intrusion or tampering on heavy equipment. It remotely alerts (via paging network or cellular link) the equipment owner or equipment supervisor when intrusion is detected. Optional practical features include engine fire detection (thermal sensing) and low vehicle battery alerts.
The present invention utilizes a novel adaptive xe2x80x9cEM Resonancexe2x80x9d technique to provide for intrusion detection. This technique provides a far greater degree of performance and lower production costs, in comparison to prior art intrusion detection methods and apparatus.
With a view towards a practical application such as the protection of heavy equipment (i.e., bulldozer or excavator), a brief overview of the adaptive resonance technique will now be given. The metal frame and chassis of a piece of heavy equipment can be considered as a single electrically conductive (and usually magnetically permeable) mass having certain electromagnetic characteristics. These characteristics would normally be fairly easily definable and hence usable for intrusion detection via various electromagnetic means (i.e., if the equipment structure was electrically isolated from its surroundings). However, most such pieces of heavy equipment, including rubber-tired ones, usually have an implement or blade etc. in contact with the earth or ground when parked and at rest.
As a result, the equipment mass/structure is effectively electrically short-circuited to the earth and although the earth is not considered a very good conductor of electricity, it can range from fairly good (when very wet/or high ion content) to fairly poor (when very dry). This range of electrical conductivity is quite broad and presents a major stumbling block to using electromagnetic means for intrusion detection in such applications.
The reason for this is that the equipment mass essentially couples to, and becomes part and parcel of, what is called the radio frequency ground plane. This coupling can vary dramatically, not just due to equipment mass, size, or topology, but mainly due to ground conductivity and further, according to the frequency of any applied or incident electromagnetic energy.
In the novel method according to one embodiment of the present invention, a small amount of electromagnetic energy (RF) is emitted (radiated) into the so-called near-field space surrounding the equipment. Due to the nature of the coupling to the ground plane, this radiation pattern is essentially omni-directional and roughly in the shape of the horizontal outline of the equipment. The energy absorbed/reflected within this field space/zone is a function of the frequency of the EM radiation, its power and the EM susceptibility of the ground plane, as well as the presence of any nearby obstructions. Accordingly, this can vary greatly.
The amount of EM energy that is absorbed by everything (EM ambient) surrounding the emitter (antenna) is measured and continually monitored by the system. This will be at a minimum when everything is at EM resonance (we can do this because only at resonance, will half the power radiate into free space, and the other half be reflected).
Any changes in the near field conditions will affect the reflected energy, but these changes are usually only slowly time-variant or small in effect. Further, the intrusion of a fairly conductive body (such as a human) into the near-field (at ground level) will not in itself perceptibly affect reflected energy (i.e., due to varying absorption), however, contact with the equipment (or even EM coupling as through gloves) will dramatically affect reflected energy and hence, the systems resonance point.
The apparatus according to the present invention, continually adapts itself to the normal slowly time-varying EM resonance point (even due to rainfall etc.) and it does this many times per second. It is immune to false triggering caused by ambient changes and even to animals brushing against the equipment. However, tampering attempts involving the use of tools (i.e., hydraulic cylinder or implement detachment) will cause a sufficiently rapid and gross enough EM resonance shift to trigger the system.
Although generically speaking, the method and apparatus according to the present invention falls under the heading of RF proximity sensing or detection, there appears to be no prior art anticipating the use of adaptive resonance means.
Further, according to another embodiment of the present invention, there is shown the use of a two-way paging network (or cellular network) for the wireless notification of disturbances/intrusions/tampering, power line carrier based communications with fire/temperature sensors, a starter disabling attachment, and a visible dye/radioactive marker attachment.
Aside from the application towards heavy equipment, the present invention has application and promise for the followingxe2x80x94boats (with large metallic sub-structures), grounded metal fencing, grounded metal buildings/structures, and even in ground insulated domestic wood-structured housing, as an alarm therefor (i.e., if the overall structure employs metal forced-air heat ducting or metal hot water piping).